The exchanging of one fluid with another is required in a wide variety of situations, such as liquid tanks, chemical processes involving liquids and gases, and in many types of different ventilation applications. The liquid or gas content in a given space ie in a tank, chamber, retort, or building space, usually is kept within a given range of temperature, gas content, or the like, condition. In order to maintain such condition a first fluid is added, and some of the contents (the second fluid) is removed, in varying proportions.
For many reasons it is desirable to carry out all three functions, ie exhausting the second fluid, introducing the first fluid, and mixing of both fluids, by means of a single piece of apparatus.
For example the installation of forced ventilation for existing buildings such as barns and industrial buildings presents certain problems. In the first place, such buildings are built of a wide variety of materials, and with widely different designs. In many cases such buildings were not originally intended for their present purpose. In particular the housing of livestock requires the installation of ventilation. However such ventilation as has been provided in the past has been unsatisfactory in many cases. Air circulation should extend throughout the full extent of the floor area of the building. If air circulation is localized, or concentrated in certain specific areas, for example, around the ventilators themselves, then the livestock will tend to congregate there, and may injure themselves. On the other hand livestock located in parts of the building which are poorly ventilated, may become ill, due to over heating, stagnating air and the like.
In U.S. Pat. No. 4,079,665, there is proposed a ventilator which overcomes many of these disadvantages. However, it was relatively expensive to manufacture, and did not operate effectively in all weather conditions. In particular it was found to ice up during cold weather. In addition, it was relatively difficult to service and repair.